This section provides background information related to the present disclosure which is not necessarily prior art.
An example of a device for providing a compensated measurement of the level of a liquid in a tank is disclosed in the international patent application publication no. WO 2005/038415. The device in WO 2005/038415 comprises a transducer for transmitting and receiving acoustic signals, and a waveguide connected to the transducer and extending into the liquid. The liquid level is basically determined based on the speed of sound and the transit time of the acoustic signal from the transducer to a surface of the liquid (where it is reflected) and back to the transducer again. Since the speed of sound depends on gas composition and temperature which may vary from time to time, the current speed of sound is used in determining the liquid level, which current speed of sound in turn is determined by means of a reference system in the waveguide. Further, since the gas composition and temperature in the reference system may differ from the gas composition and temperature in the rest of the waveguide above the liquid, for instance if the liquid level is low, a fuel pump associated with the tank is used to feed a flow of fluid (namely fuel) originating from the tank into a portion of the waveguide which in use is located above the liquid. The flow of fuel levels the temperature and gas composition, and consequently the speed of sound, throughout the waveguide above the liquid, which in turn allows for a more accurate measurement of the liquid level.
However, the device in WO 2005/038415 relies on the fuel pump to provide the flow of fluid, which may require extensive and costly modifications of the fuel pump and the associated tank when installing the measurement device.
An example of a device for providing a less extensive and less expensive compensated measurement of the level of a liquid in a tank is disclosed in the international patent application publication no. WO 2009/020424.
Compared to the device in WO 2005/038415, the device in WO 2009/020424 e.g. comprises collecting means having a liquid catching surface or opening for collecting free-moving portions of liquid, and directing means having an opening into the waveguide for directing fluid originating from liquid collected by the collecting means into or along a portion of the waveguide which during operation is located above the liquid level. The liquid catching surface or opening is larger than the opening of the directing means.
It has been seen that known devices may adapt slowly to changes in composition of gas and/or temperature leading to a non-optimal levelling out effect of the speed of sound. The delay in levelling effect of the speed of sound implies an undesirable inaccuracy in the acoustic measurements by the devices.
Thus, there is still a need in the art to provide a device for providing a compensated acoustic measurement of the level of a liquid in a tank which allows for more accurate acoustic measurements.